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MySQL temporary vs memory table in stored procedures

问题描述:

What's is better to use in a stored procedure: a temporary table or a memory table?

The table is used to stored summary data for reports.

Are there any trade offs that developers should be aware off?

CREATE TEMPORARY TABLE t (avg (double));

or

CREATE TABLE t (avg (double)) ENGINE=MEMORY;

网友答案:

Of the two, I'd use a temporary table for report.

A memory table holds data across user sessions & connections, so you'd have to truncate it every time to make sure you wouldn't be using data from someone else. Assuming you put in whats necessary to maintain a memory table depending on your needs, it's fine - the temp table is a little safer from a maintenance perspective.

网友答案:

Why is this restricted to just the two options? You can do:

CREATE TEMPORARY TABLE t (avg double) ENGINE=MEMORY;

Which works, although I'm not sure how to check if the memory engine is actually being used here.

网友答案:

A temporary table will only exist for the duration of your session. A table declared with Engine=Memory will persist across user sessions / connections but will only exist in the lifetime of the MySQL instance. So if MySQL gets restarted the table goes away.

网友答案:

In MySQL, temporary tables are seriously crippled:

http://dev.mysql.com/doc/refman/5.6/en/temporary-table-problems.html

You cannot refer to a TEMPORARY table more than once in the same query.
For example, the following does not work:

mysql> SELECT * FROM temp_table, temp_table AS t2;
ERROR 1137: Can't reopen table: 'temp_table'
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